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APPENDIX

317

of fuming sulphuric acid on anlhraquinone, the main product is
^-anthraquinone monostilphonic acid.

By fusion oi the sodium salt with caustic soda and potassium
chlorate, the hyclroxyl groups enter the a and (3 position. The
constitution of alizarin is therefore

Oil

Oil

Alizarin.

The constitution has been determined by its synthesis from
phthalic anhydride and catechol in presence of concentrated
sulphuric acid (Baeyer),

/OH    i             /CO,          /OH    i

:BH/           = C6H/      >C6H,/

NDH  2           xx)/       x)n  2

Other colouring matters have been obtained by the oxidation of
alizarin (purpurin), and by fusion of the disulphonic acids of
anthraquinone with caustic soda (anthrapurpurin and flavo-
purpurin). It is an interesting fact that, among the numerous di-
and poly-hydroxyanthraqui nones, only those which have the two
hydroxyls in the aft position are colouring matters (Liebermann
and Kostanecki),

/co\

Oil

OH

uo/

/CO,

on

; OH

OH

Purpuvin.

no

Anthrapurpurin.

OH
[OH

\/\CQ/\/
Flavupurpurin^